Piezoelectric vibrator and ultrasonic motor having piezoelectric vibrator

ABSTRACT

A piezoelectric vibrator and an ultrasonic motor having the piezoelectric vibrator. A piezoelectric vibrator has a multilayered piezoelectric actuator, with special internal and surface electrodes making the body vibrate in a longitudinal and bending direction when an electrical signal is inputted. It can be manufactured using conventional multilayer piezoelectric actuator manufacturing techniques, therefore, it has reduced manufacturing time and cost, as it is not necessary to go through two polarization processes, and may simplify and decrease the volume, while improving the vibration performance.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.2005-42711 filed with the Korea Industrial Property Office on May 20,2005, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a piezoelectric vibrator and anultrasonic motor having the piezoelectric vibrator, more specifically toa piezoelectric vibrator and an ultrasonic motor having thepiezoelectric vibrator that have simple compositions and small volumesand can improve vibration performance.

2. Description of the Related Art

Recently, the ultrasonic motor has received attention as a motor thatdoes not require wound coils, to be suitable, for example, fordecreasing the size of a device. The ultrasonic motor is widely used, asit entails low power consumption, has a light weight, provides linearmotion directly without gears, allows the control of speed and positionelectrically, and allows movement in either the forward or reversedirection.

FIG. 1 is a plan view of a piezoelectric vibrator 10 used in aconventional ultrasonic motor.

A conventional piezoelectric vibrator 10 comprises a rectangularpiezoelectric element 13 made of piezoelectric ceramic, etc., and aprotrusion part 11 formed on a side of the piezoelectric element 13. Theprotrusion part 11 applies pressure on the object of vibration (notshown), where the protrusion part 11 moves the object of vibration dueto the vibration of the piezoelectric element 13. There are fourpolarization regions, i.e. a first polarization region 13 a, secondpolarization region 13 b, third polarization region 13 c, and fourthpolarization region 13 d, formed on the piezoelectric element 13, whereall polarization regions 13 a, 13 b, 13 c, 13 d have the samepolarization direction in the direction of thickness. The fourpolarization regions 13 a, 13 b, 13 c, 13 d have the same size and arearranged in two rows. On each of the four polarization regions 13 a, 13b, 13 c, 13 d is formed an electrode.

The first and fourth polarization regions 13 a, 13 d have the samepolarization direction, while the second and third polarization regions13 b, 13 c have a polarization direction opposite to that of the firstpolarization region 13 a. Also, the first and fourth polarizationregions 13 a, 13 d and the second and third polarization regions 13 b,13 c are connected respectively by a lead wire 17.

The piezoelectric element 13 vibrates in longitudinal and bendingdirections when an electric current is supplied to the first and fourthpolarization regions 13 a, 13 d. Similarly; when an electric current issupplied to the second and third polarization regions, 13 b, 13 c, thepiezoelectric element 13 vibrates in longitudinal and bending directionshowever, this time the direction of bending vibration is opposite toprevious case.

Since the conventional piezoelectric vibrator 10 has two polarizationdirections on one piezoelectric element 13, as described above, twopolarization processes are required. This entails the problems ofincreased manufacturing time and cost of the piezoelectric element. Inparticular, if the two polarization processes are performed separatelyon one piezoelectric element 13, depolarization may occur on theportions where the polarization is performed first, to consequentlylower the performance of the piezoelectric element 13.

Further, in the conventional piezoelectric vibrator 10, only one pair ofpolarization regions 13 a, 13 d positioned diagonally are excited, whilethe other pair 13 b, 13 c are not, which lowers the vibrationperformance of the piezoelectric vibrator 10. This means that a highervoltage must be supplied to improve the vibration performance of theconventional piezoelectric vibrator 10. Moreover, to improve vibrationperformance, the conventional piezoelectric vibrator 10 was used withthe piezoelectric elements 13 stacked in multiple layers, which incursthe problem of increased volume of the piezoelectric element.

Also, polarization involves supplying a high DC voltage to apiezoelectric element 13 to arrange the dipoles within the piezoelectricelement 13 into a desired orientation, and during the polarizationprocess, large amounts of stress are concentrated on the boundaries ofthe electrodes positioned in-between the stacked piezoelectric elements13. Such stress becomes a major cause of cracks later during theoperation of the piezoelectric vibrator 10, and deteriorates theproperties of the piezoelectric element 13.

SUMMARY

As a solution to the foregoing problems, an aspect of the inventionprovides a piezoelectric vibrator and an ultrasonic motor having thepiezoelectric vibrator, with which the manufacturing time and cost arereduced, as it is not necessary to go through two polarizationprocesses.

Another aspect of the invention provides a piezoelectric vibrator and anultrasonic motor having the piezoelectric vibrator, with which thevolume may be decreased, while also providing a simple composition andimproved vibration performance.

Additional aspects and advantages of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

A piezoelectric vibrator according to a first disclosed embodiment ofthe invention comprises an elastic member having a quadrilateral crosssection, and a piezoelectric element attached to each side of theelastic member and vibrating the elastic member in a longitudinaldirection and a bending direction when an electrical signal is inputted,where the piezoelectric elements may have the same size and may beshorter than the elastic member.

Since a piezoelectric vibrator having such a composition usespiezoelectric elements having a single polarization direction, themanufacturing time and cost of the piezoelectric vibrator may bereduced. In addition, since the piezoelectric elements attachedrespectively to each side of the elastic member vibrate simultaneously,the vibration performance may be improved and the volume of thepiezoelectric vibrator may be decreased. Also, since the piezoelectricelements vibrate the elastic member, a greater rigidity may be providedcompared to conventional piezoelectric vibrators.

The pair of piezoelectric elements attached to opposing sides of theelastic member may be polarized in the same direction, while the otherpair may be polarized in opposite directions. Thus, one pair ofpiezoelectric elements may make the whole vibrator body vibrate in alongitudinal direction, while the other pair of piezoelectric elementsmay make the whole vibrator body vibrate in a bending direction.Therefore, the combination of longitudinal motion and bending motion maycause an end of the elastic member to move in an elliptical trajectory.

One end of the piezoelectric element may be aligned with one end of theelastic member to concentrate the vibration on one end of the elasticmember. Further, one edge of the piezoelectric element may be trimmedand the trimmed edge may be positioned to face outward, so as to preventshort circuits between the piezoelectric elements.

Preferably, the length of the elastic member may be twice the length ofthe piezoelectric element, to maximize the vibration of the elasticmember. Since voltages with a phase difference of 90° are suppliedrespectively to the pair of piezoelectric elements attached to opposingsides of the elastic member and the other pair of piezoelectricelements, one pair may vibrate in a bending direction, and the otherpair may vibrate in a longitudinal direction.

A piezoelectric vibrator according to a second disclosed embodiment ofthe invention comprises a pair of first piezoelectric elements, havingthe same rectangular parallelepiped shape and polarized in oppositedirections, and a pair of second piezoelectric elements, having the samerectangular parallelepiped shape and respectively attached to a side ofthe first piezoelectric element, and polarized in the same direction,where the first piezoelectric elements may be longer than the secondpiezoelectric elements, and the first piezoelectric elements may vibratein a longitudinal direction while the second piezoelectric elements mayvibrate in a bending direction when electrical signals are inputted.

Since the piezoelectric vibrator according to the disclosed embodimentsof the invention uses piezoelectric elements having a singlepolarization direction, the manufacturing time and cost of thepiezoelectric vibrator may be reduced. In addition, since thepiezoelectric elements attached respectively to each side of the elasticmember vibrate simultaneously, the vibration performance may be improvedand the volume of the piezoelectric vibrator may be decreased. Also,since only the piezoelectric elements are used, the piezoelectricvibrator may be produced with greater ease in manufacture.

By aligning one end of each of the second piezoelectric elements withone end of a first piezoelectric element, the displacement may bemaximized on one end of each of the second piezoelectric elements, andby attaching each of the second piezoelectric elements to the center ofa first piezoelectric element, both ends of the second piezoelectricelement may be made to vibrate.

It may be preferable for the length of the first piezoelectric elementto be twice the length of the second piezoelectric element, to maximizethe amount of vibration of the first piezoelectric element. Also, sincevoltages with a phase difference of 90° are supplied respectively to thefirst piezoelectric elements and the second piezoelectric elements, thefirst and second piezoelectric elements may vibrate in the longitudinaland bending directions simultaneously.

A piezoelectric vibrator according to a fourth disclosed embodiment ofthe invention comprises multiple layers of piezoelectric elements havingone polarization direction, conductive electrodes formed on both facesof the piezoelectric elements and interconnected to one another, and aprotrusion part formed on a side of the piezoelectric elements, wherethe adjacent piezoelectric elements may be polarized respectively in twoopposite directions, and the electrodes may be interconnected.

Since the piezoelectric vibrator according to the fourth disclosedembodiment of the invention uses piezoelectric elements having a singlepolarization direction, the manufacturing time and cost of thepiezoelectric vibrator may be reduced. Also, since the piezoelectricelements vibrate simultaneously, the vibration performance may beimproved, and the volume of the piezoelectric vibrator may be decreased.

By supplying a 4-phase electrical signal to the conductive electrode,the magnitude of the electrical signal may be increased further.

An ultrasonic motor according to a fifth disclosed embodiment of theinvention is equipped with a piezoelectric vibrator of any of the firstto fourth disclosed embodiments, and comprises a case into which thepiezoelectric vibrator is inserted, a slider inserted into the case tobe movable in vertical directions and moving in contact with thepiezoelectric vibrator, a first pressing member for pressing thepiezoelectric vibrator towards the slider, and a second pressing memberfor pressing the slider towards the piezoelectric vibrator.

The ultrasonic motor according to the fifth disclosed embodiment of theinvention has a decreased volume, and can increase the amount ofvibration with a lower voltage. Also, since the piezoelectric vibratorand the slider are held together steadily by the first and secondpressing members, the vibration of the piezoelectric vibrator isefficiently transferred to the slider.

The first pressing member may have a circular cross section and may bepressed towards the sliders by a flat spring inserted into the case, tohold the piezoelectric vibrator and the slider together more steadily.

The case may comprise a vibrator housing part into which thepiezoelectric vibrator is inserted, slider insertion holes leading tothe vibrator housing part through which the sliders are inserted, firstpressing member fitting grooves formed on one end of the case in apre-determined depth into which the first pressing member is inserted tocontact one end of the piezoelectric vibrator, second pressing memberinsertion holes formed perpendicularly to the slider insertion holesthrough which the second pressing member is inserted to contact theslider, and spring insertion grooves formed perpendicularly to the firstpressing member fitting grooves through which the flat spring isinserted to contact the first pressing member.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the disclosed embodiments, taken inconjunction with the accompanying drawings of which:

FIG. 1 is a plan view of a conventional piezoelectric vibrator.

FIG. 2 is a perspective view of a piezoelectric vibrator according to afirst disclosed embodiment of the invention.

FIG. 3 is a schematic diagram illustrating the polarization directionsof piezoelectric elements in a piezoelectric vibrator according to afirst disclosed embodiment of the invention.

FIG. 4 is a graph illustrating the admittances of the piezoelectricelements with respect to changes in frequency, in a piezoelectricvibrator according to a first disclosed embodiment of the invention.

FIG. 5 is an illustration using the ATILA™ software of the longitudinalvibration of a piezoelectric vibrator according to a first disclosedembodiment of the invention.

FIG. 6 a is an illustration using the ATILA™ software of the bendingvibration in the direction of the x-axis of a piezoelectric vibratoraccording to a first disclosed embodiment of the invention.

FIG. 6 b is an illustration using the ATILA™ software of the bendingvibration in the direction of the y-axis of a piezoelectric vibratoraccording to a first disclosed embodiment of the invention.

FIG. 7 is a perspective view of a piezoelectric vibrator according to asecond disclosed embodiment of the invention.

FIG. 8 is a schematic diagram illustrating the polarization directionsof piezoelectric elements in a piezoelectric vibrator according to asecond disclosed embodiment of the invention.

FIG. 9 a is an illustration using the ATILA™ software of thelongitudinal vibration of a piezoelectric vibrator according to a seconddisclosed embodiment of the invention.

FIG. 9 b is an illustration using the ATILA™ software of the bendingvibration of a piezoelectric vibrator according to a second disclosedembodiment of the invention.

FIG. 10 is a perspective view of a piezoelectric vibrator according to athird disclosed embodiment of the invention.

FIG. 11 is a schematic diagram illustrating the polarization directionsof piezoelectric elements in a piezoelectric vibrator according to athird disclosed embodiment of the invention.

FIG. 12 a is an illustration using the ATILA™ software of thelongitudinal vibration of a piezoelectric vibrator according to a thirddisclosed embodiment of the invention.

FIG. 12 b is an illustration using the ATILA™ software of the bendingvibration of a piezoelectric vibrator according to a third disclosedembodiment of the invention.

FIG. 13 is a perspective view of a piezoelectric vibrator according to afourth disclosed embodiment of the invention.

FIG. 14 is a perspective view of an example of conductive electrodes ina piezoelectric vibrator according to a fourth disclosed embodiment ofthe invention.

FIG. 15 is a schematic diagram illustrating the polarization directionsof piezoelectric elements in a piezoelectric vibrator according to afourth disclosed embodiment of the invention.

FIG. 16 a is an illustration using the ATILA™ software of thelongitudinal vibration of a piezoelectric vibrator according to a fourthdisclosed embodiment of the invention.

FIG. 16 b is an illustration using the ATILA™ software of the bendingvibration of a piezoelectric vibrator according to a fourth disclosedembodiment of the invention.

FIG. 17 is an exploded perspective view of an ultrasonic motor accordingto a fifth disclosed embodiment of the invention.

FIG. 18 is an assembled perspective view of an ultrasonic motoraccording to a fifth disclosed embodiment of the invention.

FIG. 19 is a cross-sectional view of an ultrasonic motor according to afifth disclosed embodiment of the invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described inmore detail with reference to the accompanying drawings.

FIG. 2 is a perspective view of a piezoelectric vibrator according to afirst disclosed embodiment of the invention. The piezoelectric vibrator30 according to the first disclosed embodiment comprises an elasticmember 31, having a constant length and a quadrilateral cross section,and four piezoelectric elements 33, having the same size and attachedrespectively to each side of the elastic member 31.

When an electrical signal is inputted to the piezoelectric element 33and vibration occurs, the elastic member 31 vibrates in a longitudinaldirection or a bending direction, so that consequently the end of theelastic member vibrates in an elliptical trajectory. This causes theobject of vibration (not shown) in contact with the end of the elasticmember 31 to vibrate, due to the frictional force with the elasticmember 31.

The elastic member 31 may be made from any material having elasticforce, for example, brass or stainless steel, etc. It is preferable thatthe length of the elastic member 31 be twice the length of thepiezoelectric elements to maximize the vibration generated on theelastic member 31. Also, as illustrated in FIG. 2, by aligning thepiezoelectric elements 33 with one end of the elastic member 31, thevibration generated on the other end of the elastic member 31 may bemaximized.

Although in the first disclosed embodiment the elastic member 31 isdescribed as having a quadrilateral cross section, the present inventionis not thus limited, and an elastic member 31 having any cross sectionmay be used that can vibrate in the longitudinal direction or bendingdirection using the vibration of the piezoelectric elements 33. Forexample, an elastic member may be used that has an octagonal crosssection, with the neighboring piezoelectric elements positionedrespectively on each side of the elastic member arranged to haveopposite polarization directions.

All of the piezoelectric elements 33 have the same size and are attachedrespectively on each side of the elastic member 31 by means of epoxyresin, etc. The length of the piezoelectric elements 33 corresponds tohalf the length of the elastic member 31. Also, when the piezoelectricelements 33 are attached respectively to each side of the elastic member31, as shown in FIG. 2, the assembled cross section of the fourpiezoelectric elements 33 forms a quadrilateral. The thickness of thepiezoelectric elements 33 is determined depending on the size and shapeof the piezoelectric elements 33.

The piezoelectric element 33 is formed from a material having apiezoelectric effect (a piezoelectric material). Suitable examples mayinclude PZT-based ceramics and PbTiO3-based ceramics, etc. Suitableexamples of PZT-based ceramics may include PZT andPb(Ni⅓Nb⅔)O3-Pb(Zn⅓Nb⅔)O3-PbTiO3-PbZrO3 ceramics. The piezoelectricelement 33 has unique vibration characteristics, where a strongvibration is generated when the frequency of the electrical signalinputted to the piezoelectric element 33 coincides with thecharacteristic frequency of the piezoelectric element.

A conductive electrode (not shown) is attached on one face of thepiezoelectric element 33, and the electrical signal is inputted to theelectrode. On one face of the piezoelectric element 33 is formed apolishing part 35, trimmed by mechanical processing, etc. This preventsshort circuits between the electrodes of each of the adjoiningpiezoelectric elements 33.

FIG. 3 is a schematic diagram illustrating the polarization directionsof piezoelectric elements 33 in a piezoelectric vibrator 30 according tothe first disclosed embodiment of the invention.

As shown in FIG. 3, one pair of piezoelectric elements 33 attached toopposing sides of the elastic member 31 are polarized in the samedirection, to vibrate in a bending direction with the input of anelectrical signal. Also, the other pair of piezoelectric elements 33attached to opposing sides of the elastic member 31 are polarized inopposite directions, to vibrate in a longitudinal direction with theinput of an electrical signal. Electrical signals having a phasedifference of 90° are inputted to each pair of the piezoelectricelements. For example, a voltage having a frequency of sin ωt (where ωis angular frequency) may be supplied to the pair of piezoelectricelements polarized in the same direction, while a voltage having afrequency of cos ωt (where ω is angular frequency) may be supplied tothe pair of piezoelectric elements polarized in opposite directions.

As seen in FIG. 3, the piezoelectric element 33 has a singlepolarization direction, unlike the conventional piezoelectric element13, to provide the advantages of easy manufacture of the piezoelectricelement and low manufacturing cost. Moreover, as will be describedhereafter, since all of the piezoelectric elements 33 are excited duringthe vibration of the piezoelectric vibrator 30, the magnitude of thevibration may be increased.

FIG. 4 is a graph illustrating the admittances of the piezoelectricelements with respect to changes in frequency of the signals supplied toa piezoelectric vibrator 30 according to the first disclosed embodiment.Here, the elastic member 31 is made of brass, having a length of 8.0 mmand a square cross section with a length of 0.7 mm for each side. Thepiezoelectric elements have a length of 4.0 mm, a width of 1.0 mm, and athickness of 0.3 mm. In FIG. 4, the horizontal axis represents thefrequency of the signals supplied to the piezoelectric element 33, andthe vertical axis represents the admittance, in units of

$S = {{\frac{A}{V}\lbrack{siemens}\rbrack}.}$Also, in FIG. 4, one of the overlapping curves that has two peaks around110 kHz and 200 kHz represents the admittance measured by an impedanceanalyzer for the pair of piezoelectric elements polarized in oppositedirections and the peaks represent second and third bending modes, whilethe other overlapping curve that has single peak at around 200 kHzrepresents the admittance of the other pair of piezoelectric elementspolarized in the same direction and the single peak represent firstlongitudinal mode. The curve above the two overlapping curves is thetotal admittance of the vibrator, where first longitudinal and thirdbending modes are combined around 200 kHz.

The higher the admittance of the piezoelectric element 33, i.e. thelower the impedance of the piezoelectric elements, the greater is thevibration of the piezoelectric elements 33. As seen in FIG. 4, theadmittances of the piezoelectric elements 33 increase drastically atcertain frequencies, and these frequencies at which the vibrations ofthe piezoelectric elements 33 increase drastically are the resonancefrequencies.

Table 1 was formed using the ATILA™ software to represent the resonancefrequencies (Fr) at which the admittances increase drastically, theanti-resonance frequencies, the electromechanical coupling, and thevibration directions in FIG. 4.

TABLE 1 Electromechanical Direc- Resonance Mode Fr (Hz) Fa (Hz) Coupling(%) tion first bending 36307.5 36307.8 0.37 B1_x first bending 36307.536417.4 7.76 B1_y second bending 119642 119645 0.69 B2_y second bending119642 120819 13.92 B2_x first longitudinal 198706 199284 7.61 L1 thirdbending 199335 199393 2.43 B3_x third bending 199335 201690 15.24 B3_y

As seen in FIG. 4 and Table 1, the piezoelectric vibrator 30 accordingto the first disclosed embodiment vibrates drastically in the bendingdirection at resonance frequencies Fr=36307.5, 119642, and 199335 (Hz),and vibrates drastically in the longitudinal direction at Fr=198706(Hz). Here, since the frequency range for the third bending and firstlongitudinal vibrations are very similar, electrical signals of thisfrequency are supplied to the piezoelectric elements 31 to generatevibration.

Here, since the frequency range for the third bending and firstlongitudinal vibrations are very similar, the piezoelectric elements 31vibrate in the bending direction and the longitudinal direction,simultaneously. In addition, since the electromechanical coupling is thegreatest for the third bending and first longitudinal vibrations,maximum mechanical vibration may occur with electrical signals havingthe same magnitude. Electromechanical coupling represents the conversionrate between electrical and mechanical energy, and when a largemechanical output (e.g. displacement) is generated for a certainelectrical input, it may be said that there is large electromechanicalcoupling.

FIG. 5 is an illustration using the ATILA™ software of the longitudinalvibration of the piezoelectric vibrator 30 according to the firstdisclosed embodiment of the invention, and FIGS. 6 a and 6 b are graphsillustrating the bending vibration of the piezoelectric vibrator 30.

When an electrical signal is inputted to the piezoelectric vibrator 30,the elastic member 33 vibrates in the longitudinal direction (L1longitudinal) through repetitions of elongation and contraction, asshown in FIG. 5. Here, the frequency number, found using the ATILA™software, is Fr=198706 (Hz). Also, when a frequency of Fr=199335 (Hz) isinputted, the elastic member 33 undergoes a B3 bending motion with threebends, as shown in FIGS. 6 a and 6 b. Due to the combination of the L1longitudinal and the B3 bending vibrations, one end of the elasticmember 31 vibrates in an elliptical trajectory.

In the piezoelectric vibrator 30 according to the first disclosedembodiment of the invention, all of the piezoelectric elements 33vibrate when an electrical signal is inputted, unlike conventionalpiezoelectric elements, so that not only can the vibration be increased,but also the volume of the piezoelectric vibrator may be decreased.

FIG. 7 is a perspective view of a piezoelectric vibrator 40 according toa second disclosed embodiment of the invention. Referring to FIG. 7, thepiezoelectric vibrator 40 according to the second disclosed embodimentcomprises first piezoelectric elements 41 having a pair of piezoelectricelements 41 a, 41 b of equal size, and second piezoelectric elements 43having a pair of piezoelectric elements 43 a, 43 b of a shorter lengthcompared to the first piezoelectric elements 41.

The first piezoelectric elements 41 are formed by stacking the pair ofidentical piezoelectric elements 41 a, 41 b. The first piezoelectricelement 41 is formed from the same piezoelectric ceramics as thepiezoelectric element 33 of the first embodiment described above. Aconductive electrode (not shown) is formed in-between the firstpiezoelectric element 41, which supplies electrical signals inputtedfrom an outside source to the first piezoelectric element 41. Also, theattachment surface of the first piezoelectric element 41 is grounded.One end of the first piezoelectric element 41 is in contact with theobject of vibration (not shown) to transfer driving power to the objectof vibration by means of the longitudinal and bending vibrations.

The second piezoelectric elements 43 are formed as a pair of identicalpiezoelectric elements 43 a, 43 b are each attached to a face of thefirst piezoelectric elements 41 a, 41 b by means of epoxy resin, etc. Inthe piezoelectric vibrator 40 of the second disclosed embodiment, oneend of the second piezoelectric elements 43 is aligned with one end ofthe first piezoelectric elements 41. Therefore, similar to the elasticmember 31 of the first disclosed embodiment, only one end of the firstpiezoelectric elements 41 vibrate and transfer vibrational force to theobject of vibration.

The second piezoelectric elements 43 are formed from piezoelectricceramics, with the same thickness and width as the first piezoelectricelements 41. Also, forming the second piezoelectric elements 43 to havehalf the length of the first piezoelectric elements 41 may maximize thevibration. Conductive electrodes (not shown) are formed on the upper andlower faces of the second piezoelectric elements 43, by which electricalsignals supplied from an outside source is transferred to the secondpiezoelectric elements 43.

FIG. 8 is a schematic diagram illustrating the polarization directionsof piezoelectric elements 41, 43 in the piezoelectric vibrator 40according to the second disclosed embodiment of the invention. Referringto FIG. 8, the first piezoelectric elements 41 are polarized in oppositedirections, and the second piezoelectric elements 43 are polarized inthe same direction. When electrical signals having a phase difference of90° are inputted to the first piezoelectric elements 41 and secondpiezoelectric elements 43, the first piezoelectric elements 41 make thewhole stator body vibrate in the longitudinal direction, while at thesame time the second piezoelectric elements 43 make the whole statorbody vibrate in the bending direction. Thus, due to the combination ofthe longitudinal and bending vibrations, both ends of the firstpiezoelectric elements 41 vibrate in an elliptical trajectory.

FIGS. 9 a and 9 b are graphs using the ATILA™ software to illustrate thevibration of the piezoelectric vibrator according to the seconddisclosed embodiment of the invention. As seen in FIGS. 9 a and 9 b, thepiezoelectric vibrator 40 according to the second disclosed embodimentis capable of L1 longitudinal and B3 bending vibrations, as in the firstdisclosed embodiment.

With regards the piezoelectric elements 41, 43 in the piezoelectricvibrator 40 according to the second disclosed embodiment, it is seenthat the manufacture of the piezoelectric elements is made easier, aseach piezoelectric element 41 a, 41 b, 43 a, 43 b has the samepolarization direction. Also, since the first piezoelectric elements 41and the second piezoelectric elements 43 vibrate simultaneously, thepiezoelectric vibrator may have a simple structure, with improvedvibration performance, while the volume of the piezoelectric vibrator 40may be decreased. Further, with the piezoelectric vibrator 40 accordingto the second disclosed embodiment, vibration is generated by thepiezoelectric elements 41, 43 only, to allow high efficiency and easymanufacture.

FIG. 10 is a perspective view of a piezoelectric vibrator 40′ accordingto a third disclosed embodiment of the invention. Referring to FIG. 10,the piezoelectric vibrator 40′ according to the third disclosedembodiment comprises first piezoelectric elements 41′ having a pair ofpiezoelectric elements 41 a′, 41 b′ of equal size, and secondpiezoelectric elements 43′ having a pair of piezoelectric elements 43a′, 43 b′ of a shorter length compared to the first piezoelectricelements 41′.

The composition of the first piezoelectric elements 41′ and the secondpiezoelectric elements 43′ are identical to the first piezoelectricelements 41 and the second piezoelectric elements 43 in thepiezoelectric elements of the second disclosed embodiment describedabove. The difference from the second disclosed embodiment is that thesecond piezoelectric elements 43′ are positioned at the center of thefirst piezoelectric elements 41′.

The lengthwise center of the second piezoelectric elements 43′ coincideswith the lengthwise center of the first piezoelectric elements 41′.Therefore, when electrical signals are inputted to the firstpiezoelectric elements 41′ and the second piezoelectric elements 43′,both ends of the first piezoelectric elements 41′ vibrate in ellipticaltrajectories.

FIG. 11 is a schematic diagram illustrating the polarization directionsof the piezoelectric elements 41′, 43′ in the piezoelectric vibrator 40′according to the third disclosed embodiment of the invention. Referringto FIG. 11, the first piezoelectric elements 41′ are polarized inopposite directions, and the second piezoelectric elements 43′ arepolarized in the same direction, which is the same as the polarizationdirections of the piezoelectric elements of the second disclosedembodiment.

FIGS. 12 a and 12 b are illustrations using the ATILA™ software of thevibration of the piezoelectric vibrator 40′ according to the thirddisclosed embodiment. As illustrated in FIGS. 12 a and 12 b, thepiezoelectric vibrator 40′ according to the third disclosed embodimentundergoes L1 longitudinal and B3 bending vibrations, as do thepiezoelectric vibrators of the first and second disclosed embodimentsdescribed above. Both ends of the first piezoelectric elements 41′vibrate simultaneously in elliptical trajectories.

With regards the piezoelectric elements 41′, 43′ in the piezoelectricvibrator 40′ according to the third disclosed embodiment, it is seenthat the manufacture of the piezoelectric elements is made easier, aseach piezoelectric element 41 a′, 41 b′, 43 a′, 43 b′ has the samepolarization direction. Also, since the first piezoelectric elements 41′and the second piezoelectric elements 43′ vibrate simultaneously, thepiezoelectric vibrator may have a simple structure, with improvedvibration performance, while the volume of the piezoelectric vibrator40′ may be decreased. Further, with the piezoelectric vibrator 40′according to the second disclosed embodiment, vibration is generated bythe piezoelectric elements 41′, 43′ only, to allow high efficiency andeasy manufacture.

FIG. 13 is a perspective view of a piezoelectric vibrator 50 accordingto a fourth disclosed embodiment of the invention. The piezoelectricvibrator 50 according to the fourth disclosed embodiment comprisesidentical piezoelectric elements 51 stacked in multiple layers,conductive electrodes 53 formed between the piezoelectric elements 51,and a protrusion part 55 protruded from one side of the piezoelectricelements 51.

The piezoelectric elements 51 have equal sizes and are stacked inmultiple layers. The piezoelectric elements 51 are formed from the samepiezoelectric ceramics as in the piezoelectric elements 33, 41, 41′ ofthe first to third disclosed embodiments described above. Electrodes areformed on both faces of the piezoelectric element 51 which supplyelectrical signals to the piezoelectric element 51. Although in FIG. 13the piezoelectric elements 51 are formed in seven layers, the presentinvention is not thus limited, and a stack of six or less or eight ormore layers may be used, depending on the size of the piezoelectricelements 51 and desired amount of vibration, etc.

The protrusion part 55 protrudes from a side of the piezoelectricelement 51 to the exterior by a predetermined length. The protrusionpart 55 vibrates in an elliptical trajectory, due to the vibration ofthe piezoelectric elements 51 in the longitudinal and bendingdirections. As the protrusion part 55 is in contact with the object ofvibration (not shown), the object of vibration is made to vibrate bymeans of the protrusion part 55.

Since the protrusion part 55 transfers driving power using frictionalforce with the object of vibration, a wear-resistant member may beformed on the protrusion part 55. The wear-resistant member may includevarious materials containing glass materials, such as soda, lead,borates (e.g. Pyrex™), crowns, flint, heavy flint, and quartz glass,etc., or ceramic materials, such as alumina, zirconium oxides, siliconcarbides, silicon nitrides, tungsten carbide, and titanium carbide, etc.

FIG. 14 is a perspective view of an example of the conductive electrodes53 in the piezoelectric vibrator 50 according to the fourth disclosedembodiment of the invention. Referring to FIG. 14, the electrodes 53include an upper electrode 53 a formed on the uppermost face of thepiezoelectric elements 51, a lower electrode 53 b formed on thelowermost face, and a first to sixth inner electrodes 53 c 1, 53 c 2, 53c 3, 53 c 4, 53 c 5, 53 c 6 stacked orderly on the faces of thepiezoelectric elements 51.

As shown in FIG. 14, the upper electrode 53 a and the second innerelectrode 53 c 2 have identical patterns, and the first inner electrode53 c 1 and the third inner electrode 53 c 3 have identical patterns.Also, the fourth inner electrode 53 c 4 and the sixth inner electrode 53c 6 have identical patterns, and the fifth inner electrode 53 c 5 andthe lower electrode 53 b have identical patterns. Further, the firstinner electrode 53 c 1 and third inner electrode 53 c 3 have a patternsymmetrical to the fourth inner electrode 53 c 4 and sixth innerelectrode 53 c 6 in the length and width directions of the electrodes.Also, the upper electrode 53 a and second inner electrode 53 c 2 aresymmetrical to the lower electrode 53 b and fifth inner electrode 53 c 5in the length and width directions of the electrodes. The upperelectrode 53 a, the lower electrode 53 b and the first to sixth innerelectrodes 53 c 1, 53 c 2, 53 c 3, 53 c 4, 53 c 5, 53 c 6 are used topolarize the piezoelectric element 51 and supply electrical signals. Theelectrodes 53 according to the fourth disclosed embodiment are notlimited to those shown in FIG. 14, and it is apparent that a variety ofmodifications may be made by the skilled person.

Sin and −sin are inputted to the upper electrode 53 a, and cos and −cosare inputted to the lower electrode 53 b. Thus, electrical signalshaving four phases are inputted to the piezoelectric vibrator 50according to the fourth disclosed embodiment. Since sin and −sin and cosand −cos are inputted to the upper electrode 53 a and the lowerelectrode 53 b, the input of electrical signals with a relativemagnitude of 2 sin (or 2 cos) may be effected.

FIG. 15 is a schematic diagram illustrating the polarization directionsof piezoelectric elements 51 in the piezoelectric vibrator 50 accordingto the fourth disclosed embodiment. As shown in FIG. 15, all adjacentpiezoelectric elements 51 are polarized in opposite directions. Also,each of the piezoelectric elements 51 has one polarization direction.

FIGS. 16 a and 16 b are illustrations using the ATILA™ software of thevibration of the piezoelectric vibrator 50 according to the fourthdisclosed embodiment. As shown in FIGS. 16 a and 16 b, the piezoelectricvibrator 50 according to the fourth disclosed embodiment vibrates in thelongitudinal direction at 265 kHz, and vibrates in B2 mode in thebending direction at 267 kHz. Therefore, as the frequency band rangesare the same, the piezoelectric vibrator 50 vibrates simultaneously.

Since all of the piezoelectric elements 51 in each layer of thepiezoelectric vibrator 50 according to the fourth disclosed embodimenthave a uniform polarization direction, it is seen that the manufactureof the piezoelectric elements is made easier. Moreover, since all of thepiezoelectric elements 51 vibrate simultaneously, the piezoelectricvibrator may have a simple structure, with improved vibrationperformance, while the volume of the piezoelectric vibrator 50 may bedecreased.

Hereinafter, an ultrasonic motor 70 according to a fifth disclosedembodiment of the invention will be described with reference to FIGS. 17to 19.

FIG. 17 is an exploded perspective view of the ultrasonic motor 70according to the fifth disclosed embodiment of the invention, and FIG.18 is a perspective view representing the ultrasonic motor 70illustrated in FIG. 17 in its assembled state. FIG. 19 is an assembledcross-sectional view of the ultrasonic motor of FIGS. 17 and 18.

Referring to FIG. 17, an ultrasonic motor 70 based on an aspect of thepresent invention comprises a case 71, a piezoelectric vibrator 80inserted into the case, a first pressing member 73 pressing the rear endof the piezoelectric vibrator 80, second pressing members 75 pressingthe sliders 79 a, 79 b, and a flat spring 77 pressing the first pressingmember 73.

The case 71 houses the piezoelectric vibrator 80, first pressing member73, second pressing members 75, flat spring 77, and sliders 79 a, 79 b.The case 71 comprises a vibrator housing part 715 into which thepiezoelectric vibrator 80 is inserted, slider insertion holes 713holding the sliders 79 a, 79 b, first pressing member fitting grooves717 into which the first pressing member 73 is inserted, second pressingmember insertion holes 711 through which the second pressing members 75are inserted, and spring insertion grooves 719 through which the flatspring 77 is inserted.

The vibrator housing part 715 is formed in the center of the case 71.Although both ends of the piezoelectric vibrator 80 are isolated by thecase 71 from the exterior, the other parts are exposed to the exterior.The piezoelectric vibrator 80 is inserted into and fixed in the vibratorhousing part 715. The slider insertion holes 713 lead to the vibratorhousing part 715.

A portion of the sliders 79 a, 79 b is inserted through the sliderinsertion holes 713. Since the diameter of the slider insertion holes713 is somewhat greater than the diameter of the sliders 79 a, 79 b, thesliders 79 a, 79 b may freely ascend and descend. The slider insertionholes 713 lead to the vibrator housing part 715 and are formedperpendicularly to the second pressing member insertion holes 711.

Both ends of the second pressing members 75 a, 75 b are inserted throughthe second pressing member insertion holes 711. The first pressingmember fitting grooves 717 are grooves formed at one end of the case 71in the length direction having the shape of slots with the ends on oneside open. The first pressing member 73 is fitted into the firstpressing member fitting grooves 717 to press the rear side of thepiezoelectric element 80 inserted into the vibrator housing part 715.The spring insertion grooves 719 are grooves formed on the case 71 in avertical direction, and the flat spring 77 inserted into the springinsertion grooves 719 presses the first pressing member 73.

A piezoelectric vibrator 30, 40, 40′ 50 according to the first to fourthdisclosed embodiments may be used for the piezoelectric vibrator 80. Aprotrusion part 81 is formed on one end of the piezoelectric vibrator80, where the protrusion part 81 moves the sliders 79 a, 79 b invertical directions using frictional force. The composition of thepiezoelectric vibrator 80 is the same as in the first to fourthdisclosed embodiments, so that detailed explanations are omitted.

The sliders 79 include a first slider 79 a inserted through the sliderinsertion holes 713 to contact the protrusion part 81 of thepiezoelectric element 80, and a second slider 79 b which guides thefirst slider 79 a to prevent it from rotating. Since the first slider 79a, as shown in FIG. 19, is in contact with the protrusion part 81 of thepiezoelectric vibrator 80, it moves in vertical directions due to thevibration of the protrusion part 81.

The first pressing member 73 is a rod having a circular cross section.The first pressing member 73, as shown in FIG. 19, is in line-contactwith the piezoelectric vibrator 80. Thus, the first pressing member 73may press the piezoelectric vibrator 80 exactly perpendicularly. Thefirst pressing member 73 is prevented from being dislodged from thefirst pressing member fitting grooves 717 by the flat spring 77.

The second pressing members 75 are rods having circular cross sectionsinserted through the second pressing member insertion holes 711 and, asshown in FIG. 19, presses the first slider 79 a towards thepiezoelectric vibrator 80. The second pressing members 75 may be formedin numbers of three or greater. The flat spring 77 presses the firstpressing member 73 towards the sliders 79 by means of elastic force.Thus, the protrusion part 81 of the piezoelectric vibrator 80 and thefirst slider 79 a are always in contact.

While the spirit of the invention has been described in detail withreference to particular embodiments, the embodiments are forillustrative purposes only and do not limit the invention. It is to beappreciated that those skilled in the art can change or modify theembodiments without departing from the scope and spirit of theinvention.

According to an aspect of the present invention, the embodiments ofwhich are as set forth above, a piezoelectric vibrator and an ultrasonicmotor having the piezoelectric vibrator may be provided, with which themanufacturing time and cost are reduced, as it is not necessary to gothrough two polarization processes.

According to another aspect of the present invention, a piezoelectricvibrator and an ultrasonic motor having the piezoelectric vibrator maybe provided, with which the decline in performance due to thedepolarization of the piezoelectric elements is removed.

According to yet another aspect of the present invention, apiezoelectric vibrator and an ultrasonic motor having the piezoelectricvibrator may be provided, with the volume decreased and the vibrationperformance improved.

1. An ultrasonic motor comprising: a piezoelectric vibrator, comprisingan elastic member having a quadrilateral cross section; andpiezoelectric elements, attached to each side of the elastic member andvibrating the elastic member in a longitudinal direction and a bendingdirection when an electrical signal is inputted, wherein thepiezoelectric elements have the same size and are shorter than theelastic member; a case, into which the piezoelectric vibrator isinserted; a slider, inserted into the case to be movable in verticaldirections, and moving in contact with the piezoelectric vibrator; afirst pressing member to press the piezoelectric vibrator towards theslider; and a second pressing member to press the slider towards thepiezoelectric vibrator.
 2. The ultrasonic motor of claim 1, wherein thepiezoelectric elements comprise two pairs of piezoelectric elements, onepair of piezoelectric elements being attached to opposing sides of theelastic member and polarized in the same direction, and the other pairbeing polarized in the opposite directions.
 3. The ultrasonic motor ofclaim 1, wherein one end of the piezoelectric elements are aligned withone end of the elastic member.
 4. The ultrasonic motor of claim 1,wherein one edge of each of the piezoelectric elements is trimmed, andthe piezoelectric elements are positioned with the trimmed edge facingoutward.
 5. The ultrasonic motor of claim 1, wherein the length of theelastic member is twice the length of the piezoelectric elements.
 6. Theultrasonic motor of claim 1, wherein voltages with a phase difference of90° are supplied respectively to the one pair of piezoelectric elementsattached to opposing sides of the elastic member and the other pair ofpiezoelectric elements.
 7. The ultrasonic motor of claim 1, furthercomprising a flat spring inserted into the case, wherein the firstpressing member has a circular cross section and is pressed towards thesliders by the flat spring inserted into the case.
 8. The ultrasonicmotor of claim 7, wherein the case comprises: a vibrator housing partinto which the piezoelectric vibrator is inserted; slider insertionholes leading to the vibrator housing part through which the sliders areinserted; first pressing member fitting grooves formed on one end of thecase in a predetermined depth into which the first pressing member isinserted to contact one end of the piezoelectric vibrator; secondpressing member insertion holes formed perpendicularly to the sliderinsertion holes through which the second pressing member is inserted tocontact the slider; and spring insertion grooves formed perpendicularlyto the first pressing member fitting grooves through which the flatspring is inserted to contact the first pressing member.